feat: add diagnostic commands to nix workflow

In the nix workflow, several diagnostic commands are added prior to the docker login attempt. This includes echoing the $PATH, checking the docker location with 'which', and listing /bin directory's contents. These are intended to troubleshoot potential issues in the continuous integration environment.

.forgejo/workflows/nix.yaml

@@ -7,8 +7,11 @@ jobs:
       - run: nix build -L .#runner
       - name: upload image
         run: |
+          echo $PATH
+          which docker
+          ls -al /bin
           docker login -u ${{ secrets.REG_USER }} -p ${{ secrets.REG_TOKEN }} ${{ secrets.CI_REGISTRY }}
-          export IMAGE_TAG=$(docker load < result | grep -Po 'Loaded image.*: \K.*')
+          export IMAGE_TAG=$(docker load -i result | grep -Po 'Loaded image.*: \K.*')
           echo "Pushing image ${IMAGE_TAG}"
           docker tag "${IMAGE_TAG}" "${{ secrets.CI_REGISTRY }}/${{ secrets.REG_USER }}/nix-runner:latest"
           docker push "${{ secrets.CI_REGISTRY }}/${{ secrets.REG_USER }}/nix-runner:latest"